A measurement of the surface energy anisotropy of nickel by transmission electron microscopy of field emitter crystals

Abstract

A combination of field emission (FEM) and transmission electron microscopy (TEM) is used to measure the anisotropy of the surface tension (γ) of a metal (nickel). The stationary form of a clean nickel tip is produced and controlled in a field electron microscope, under ultrahigh vacuum. The shape of the tip is visualized in a TEM and then analysed. It is shown that the cap around the apex of a bulbous tip closely approximates the equilibrium shape of a nickel crystal. By using the inverse Wulff construction, the anisotropy of γ can be measured as a function of crystallographic orientation. Values of γ normalized to (111) have been obtained for the 〈200〉 and the 〈2̄20〉 zones. The maximum anisotropy is found at [026] along the 〈200〉 zone ( γ 026 γ 111 = 1.05 ). The results agree with the available experimental or theoretical data reasonably well.